Colonie, New York

C.T. Male Associates was retained by New York Power Authority (NYPA) to survey and map some areas of spalling on part of the Crescent Dam structure on the Mohawk River in the Town of Colonie, New York. The dam, constructed in 1912, is located upstream of the confluence of the Mohawk and Hudson Rivers. The Dam impounds waters for hydroelectric power, drinking water and navigation purposes.

C.T. Male Associates performed a High Definition 3D Laser Scan Survey using its Lecia HDS 3600 High Definition Laser Scanner to obtain the high level of detail needed to develop a method for repair of the dam. The laser scanner produces a group of millions of highly accurate points, called a point cloud, used to create a 3-D model. The laser scan of the 526 foot long dam structure was scheduled to start in August but heavy rains delayed the start until December.

The water level was lowered below the spillway to allow access to the dam face without water flowing over it. The entire flow of the river had to be diverted through the power house to keep the water from spilling over the crest of the dam. NYPA could only lower the water level for a short time due to scheduled maintenance of hydroelectric turbines. With impending winter weather on the way and rising water levels, timing was critical.

On the day of the scan the temperature was seven degrees Fahrenheit and the laser scanner had never been used in such extremely cold weather. An inch and a half of ice had formed on some of the still backwaters of the river. Water that was seeping through the cracks in the dam produced ice sheets on the face of the dam.

The scanner was transported to the control points by rowboat while a crew member knelt in the bow of the boat chopping through inch and a half ice with a sledge hammer. The crew got stuck in one of the powerful eddies in the water current downstream of the tail race and had a difficult time getting the boat out of the swirling water. After the scan, the crew had to row back against strong late-day winds pushing them farther and farther away from shore.

The point cloud consisted of over 16 million points and was registered over a seamless panoramic digital photo allowing C.T. Male Associates engineers to visualize and quantify the cracks and spalling in the Dam. Mapping was performed in Leica’s Cloudworx and a 3-D model of the dam was created. Isometric views were mapped as well as 142 cross sections, a Digital Terrain Model (DTM) and Topographic Contour Map across the face of the dam. Some of the areas of spalling and cracks were big enough to fit a person inside of them.

The reconstruction project went out to bid to contractors and repair to the Crescent Dam began in the summer of 2009. As a result of C.T. Male Associates’ dedication to the project, the final product was detailed, comprehensive and exceeded the expectations of the client.